The enquiry is directed toward analysis of the events involved in transduction of stimulus (whether neurotransmitter, hormone or action potential) into secretory response in various cells including the endocrine cells of the adrenal medulla and pituitary glands and with comparative studies involving other secretory cells, particularly peritoneal mast cells. The focus is on calcium and exocytosis. The hypothesis being tested is that calcium-activated exocytosis is a general feature of stimulus-secretion coupling and the enquiry revolves around the sources of calcium drawn on to effect exocytosis, the mechanisms involved in calcium influx or mobilization, and the possible role of that ion as a coupling agent. The methods involve isolated cells, or tissues exposed to various ionic and pharmacological manipulations and electrophysiological analysis.